We are studying the means of oxidation of cholesterol, other sterols, other unsaturated lipids, and polycyclic aromatic hydrocarbons with mild agents which simulate conditions likely to be present in human and animal tissues so as to determine whether specific oxidation products of these components are formed. The specific oxidation products of interest are peroxide, hydroperoxide, and epoxide derivatives that have previously been demonstrated to be carcinogenic or mutagenic or which are suspected of being so. We are trying to compare the mild oxidation conditions, commonly termed autoxidative, with metabolic transformations of these same materials so as to determine whether there are both enzymic and autoxidative processes likely to contribute to the presence of these potential carcinogens in tissue.